text:
What are the aerodynamic advantages and disadvantages of the Weltensegler wing?
What are the aerodynamic advantages and disadvantages of the Weltensegler Wing?
Would this kind of wing configuration come to help for a glider?
Is there any difference between them and gull wings?
What are the aerodynamic advantages of gull wings?

those are a lot of questions. I think it might be better if you could split them in different posts

Related: What's the advantage of the F4U Corsair's gull wing design?

The inspiration for the Weltensegler wing were birds. The reason for their wing shape is structural, however, not aerodynamic. Your photo shows the 1922 version, called "Baden-Baden Stolz", which was a follow-on to the original and more ambitious version of 1921. The 3-side-view below shows the planform (picture source). However, this airplane never flew, which probably saved the life of its pilot. While pitch and limited roll control was possible with the elevons on the outer wings, no consideration was given to directional control.

The 1921 version was controlled by warping of the outer wings, the washout of which was controlled with pulleys and springs. The idea was that this would help to adjust the wing shape to flight speed. The picture below shows the first and last flight, which is historically significant as the first glider flight in which a considerable gain in height was achieved. However, it ended in a spiral dive which killed its pilot (picture source).

Weltensegler is actually the name of the company which was founded by Friedrich Wenk. Alexander Lippisch was one of his employees.
The configuration cannot be recommended for a glider. It is much better to have a straight inner wing and dihedraled outer wings, as explained in this answer. The anhedral of the outer wings of the Weltensegler wings will produce a downforce on the windward wing, rolling it into the wind which is the opposite of what is needed for coordinated flight. Other configurations using an "M"-shaped wing did so for different reasons and use rudders and much more anhedral on the outer wing panels.

Peter, generally while gliding, don't gulls have a drooped wingtip configuration? How does it help them?

@RisshiJain: I think it helps them to keep the wings outstretched without much effort. The tension part on the lower side of the wing will be more stable because it will pull the lower wing contour outward. Once the wing flips into a polyhedral shape, bones and tendons will have trouble to stay in place.

Having an anhedral in the main wing will cause it to be very laterally unstable. Most planes nowadays have a few degrees of dihedral to keep the plane stable in case of a gust of wind coming from the side. Also, this plane had no vertical stabilizer.

@alex: Note the distinctive washout in the outer panels: The Weltensegler gliders had a bell-shaped lift distribution long before the Hortens were around, and as such did not strictly need a vertical. But some sort of drag device on the outer wings would had been handy to avoid the spiral dive.

@Peter Kampf: That's exactly what I was thinking. That may have saved the pilot's life if one had been outfitted.

Modern flex-wing hang gliders can be viewed as having dihedral in the inboard parts of the wing and anhedral in the outboard parts of the wing.  Even if the "crossbar" is a straight line, and each leading edge tube is a straight line, the "billowed" shape of the trailing edge creates this geometry.  Stand some distance outboard of the wingtip, and you can invariably find a viewing position where you can see the top surface of the outboard part of the near wing, and the bottom surface of the outboard part of the far wing (ctd)

(ctd) and the bottom surface of portions of the inboard part of the near wing, and the top surface of the corresponding portions of the inboard part of the far wing.  That's a gull-shaped geometry, with dihedral inboard and anhedral outboard.  This should be made into a real answer, but would need photos to do it justice.


text:
What was the first operational U.S. military jet fighter to fly at mach 2?
Was it the McDonnell Voodoo or the Lockheed F-104A?

There is no question in the body and you seem to have answered the title question yourself.  What exactly are you asking?

Mach 2 at what altitude? And in what flight regime? Controlled horizontal, dive, uncontrolled?

According to the Federation of American Scientists website on the F-104, it was the first aircraft to fly at twice the speed of sound, and held numerous speed and altitude records. The website claims a max speed of Mach 2.2 at 35,000 feet. The same website credits the Voodoo with being the first aircraft to exceed 1000 mph in level flight, and gives a max speed of 1095 mph. However, an altitude is not quoted for this speed, so it's not possible to translate to a Mach number. At sea level, 1095 mph is Mach 1.44, and increases at higher altitudes. Note that even assuming the Voodoo could fly at its top speed of 1095mph at 35,000ft, that is still slower than the 104, for which Mach 2.2 works out at 1450 mph. See  FAS

The airplane would be the J79 powered F-104 Starfighter.

A reference or explanation of why this is the answer would be helpful.

depending on requirements, it could be the F-8 or F-101 both of which could probably hit Mach 2 in a dive... Maybe the F-100 could as well, haven't been able to find references for that.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
What model is this strange airplane-helicopter combination?
I'm a local historian in Fort Collins, CO and I'm trying to find out anything I can about the helicopter/plane image in the attached picture. The only thing I know is that it was parked in a early Fort Collins airport.

I believe that's called an autogyro.  The rotor operates in "autorotation" I.e. It is unpowered.

It is a Pitcairn PCA-2 autogiro. From the linked article:

This aircraft is a Pitcairn PCA-2 autogiro, S/N B-12 (ATC #410), manufactured in April 1931 by Pitcairn Aircraft, Inc., Willow Grove, PA. It came from the factory with a Wright J-6 engine (S/N 12528) of 300HP. It had a Hartzell steel propeller.  It was a three-place craft, weighing 3,000 pounds.

Apparently, the aircraft was owned by Amelia Earhart and sponsored by Beech-Nut packing company.

NC10780 was sold to George Palmer Putnam, husband of Amelia Earhart, of New York, NY on May 7, 1931.  This autogiro is the “older” (by a week) sister ship of NC10781 flown through Tucson by John M. Miller.

That's some mighty fine sleuthing!

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What aircraft is this flying near Greenford?
I live in the suburbs of London in Greenford (near RAF Northolt Base) and today I heard a droning sounds which, albeit from my limited experience, sounded like a propeller plane. I checked my generic flight radar application on my smart phone, no result. I then checked the ADS-B tracking website which identifies most military aircraft that aren't flying covertly but, again, no result.
I did manage to take a picture of the aircraft and it looks like a small passenger turboprop plane - so any ideas about what aircraft this is and why it wouldn't be showing up on any radars? It does not seem like a stealthy fighter jet by any means.

Was the bottom of the body bright red? (I assume your eyesight is better than mine in combination with the picture.)

Seems to be dark blue

The Let L-410 looks similar - possibly military personel transportation? I know the German airforce uses these

My guess is that it is an "old timer". Things to work on:

the wing is elliptical
the vertical tail is rounded
the engines seem to be almost as large as the cockpit
the horizontal tail seems to have some kind of simmetrical feature
it has a low tail, not a T-tail

I uploaded another image. On this one it doesn't seem so elliptical and the vertical stabiliser seems to have some sort of circle icon. I thought for a moment it might be a Britten-Norman? I guess the jury is still out.

I was going to guess Avro Anson, but there seems to be only one operative and is in New Zealand

@Federico Sorry, didn't see you guessed an Avro Anson before I posted by suggestion below! The Shuttleworth Collection owns one (according to Wikipedia), and is based in Old Warden in Bedfordshire, England. The tail section does look a bit off compared to OP's picture... the elevators looking more swept back in a right-angle sort of shape.

Sorry to bring up an old thread but what about an Embraer EMB 121 Xingu? I saw one flying today in the same area from the French Air Force.

@DanielK — it's got a T-tail so that seems unlikely — and it's got a much shorter nose than the EMB 110.

I think i found an answer. Have a look at my new answer @Federico

Spy planes!!! Looks like I found an answer after two years when I came across a blog called 'secret bases'.
"Keen MI5 spy plane spotters should continue to lurk around RAF Northolt. A company formed by former elite RAF pilots, 2 Excel Aviation, actually based at Sywell Aerodrome, Northamptonshire, is now performing those spooky Northolt tasks, as part of its Scimitar special projects team.
They are using Piper PA31 Navajo aircraft "G-SCIR" (ModeS 40729C), "G-SCTR" (ModeS 40029D) and "G-SCMR" (ModeS 40729E) — all registered to 2 Excel in February / March 2017. They joined regular "sneaky-beaky" craft "G-UMMI" (ModeS 400C86) which is regularly spotted with special communications equipment attachments.
All three RAF Northolt Piper Navajo PA31 craft had been purchased by 2 Excel from Mike Jones Aircraft Sales Inc in Murfreesboro, Tennessee, America, who specialise in Colemill Panther conversions for performance and safety boosts. G-SCTR previously carried registration mark N331DB. G-SCIR had been supplied with tail number N522AW and G-SCMR had previously carried N27773.
Military aviation enthusiast Alan Warnes blogged on the subject in August 2017 on his Warnesy's World website, but strangely he only noted two out of the three Piper Navajos and missed G-SCIR. Curious, as the three registrations all took place at the same time – February / March 2017.
The London Evening Standard's Business Pages reported on my findings in an article headlined "Lift Off: Home Office privatises MI5 spy plane operations"."

The belly paint job looks the same. I think you nailed it!

2200hrs, 7/3/20, G-SCIR is currently doing approx 20mile leg circuits centering on Hull.
https://i.sstatic.net/0XmmK.png

@bradshaw Scooping up mobile communications for analysis I wonder? Interesting :)

A long shot, but perhaps it's an Avro Anson, a true "old timer" from WWII and used by the RAF no less.

(source: wikimedia.org)
Image credits all from Wikipedia

Sorry to bring up an old thread but what about an Embraer EMB 121 Xingu? I saw one flying today in the same area from the French Air Force.

I think i found an answer. Have a look at the bottom

@quiet-flyer I think I answered the question :) it’s a Piper PA31 Navajo aircraft

I'm going to hazard a guess here, but that's likely the best you will get unless someone tracks down a photo of a plane with a matching paint scheme.
Here's my thought process:

tapered, low wings
engine nacelles are  almost as long as the nose, which narrows things down a bit
engine nacelles are relatively large in size, so it's...

probably piston engined
probably fairly small, maybe 6 passengers?

vertical tail looks swept
horizontal tail is placed low, and is at least as wide as the engine nacelles
fuselage tapers from the trailing wing root to the tail

As far as I can tell, it looks an awful lot like a Beechcraft Baron.

Image credit: AOPA

The wingtips look more tapered and the nose more boxy than the Baron to my eye, but I could well be wrong.

Yeah, could be. Without a higher quality photo, this is really just an exercise in futility. My other guess was a smaller Cessna twin, but not much lined up.

Better match than the King Air, but still: The trailing edge of the rudder looks rounded, not straight like in the Baron. I'm not convinced.

@egid: Yes, I thought for a moment it could be a Cessna T-50, but the fuselage nose is much longer. Still, the round wingtips and vertical suggest an older design, from the 40s or 50s.

@PeterKämpf I think the round tail is just blurred overexposure; note the apparent 'dent' in the left tailplane.

@Sanchises: Yes, and the blue paint job makes it harder to recognize the correct shape.

@PeterKämpf Indeed. I am under the impression that the fuselage does not extend under the tailplane, but that may very well be the paint job.

@PeterKämpf I am fairly certain the vertical is swept with a straight trailing edge. The top aft corner of it looks like it has a paint swoop... but that could also just be JPEG artifacts.

Sorry to bring up an old thread but what about an Embraer EMB 121 Xingu? I saw one flying today in the same area from the French Air Force.

@PeterKämpf I think I found the answer guys..have a look.

Given its proportions and size, as well as the shape of the wing platform, I might guess a Beech King Air C90.

to me it does not have the right shape of wings/tail

And the engine nacelles look too slender.

Sorry to bring up an old thread but what about an Embraer EMB 121 Xingu? I saw one flying today in the same area from the French Air Force.

This a piper pa-31 navajo cdg 23b, g-scir.
It flies from doncaster everynight to patrol over the english channel. On the look out for migrants coming from calais. Ive been tracking it for the last 2 days. There is also a fixed wing drone patrol which takes off and lands back at llyd airport. Nothing top secrect im happy to say. The circle people are saying they see underneath is camera with infared and nightvision just like they have on the police helicopter.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
When was the first manned rocket-propelled plane launched?
I believe that it's an issue of some interest in the history of aviation.

please define the parameters of "rocket"

There's an interesting text on the subject, freely available in the internet (in German) by Austrian rocket pioneer Max Valier. https://booksc.org/book/80611012/6a4e2a [From his book 'Raketenfahrt',  München / Oldenbourg, 1930]
Valier gives extensive and valuable details on the rocket-powered glider that was possibly the first rocket-propelled vehicle to become airborne, but he also mentions a semi-legendary account of a Chinese attempt, centuries ago, by a mandarin Wan-Hu... (page 236).
A fragment of Valier's text:

Abundant details on that rocket plane follow...

rocket propelled != rocket. this is the reason the community closed the previous question. it needs more details, the definition of "rocket" that qualifies is not provided

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Can an airliner land safely using only propulsion control?
In this amazing story ,after losing all hydraulic power of the aircraft , Captain Al Haynes guided the plane to the Sioux city, crashed but saved 185 of the 296 lives (United Airlines Flight 232-Sioux City, 1989). After this incident, NASA started to work on PCA systems.

Gordon Fullerton landed an F-15, using only engine power. How did the F-15 land while the airliner crashed? Since an airliner and a fighter jet have different engine positions honestly it would make more sense to me if the airliner made it to the ground but fighter couldn't because it has relatively greater distance between engines, so better capability of yawing and as a result of having a shorter wingspan a fighter needs to fly faster to stay airborne. I understand the weight difference, i understand the possibility of adverse weather conditions during 232 flight, but i still don't get how a fighter is more capable than an airliner.

The main assumption is flawed, there are many cases of airliners landed after an hydraulical failure

@FredLarson I did check that , but that is a test flight , I wonder what would happen in a situation where a modern airliner is fully loaded.

I think in the SUX incident they had directional control down. The problem was lack of flaps, air brakes, spoilers, brakes or reverse thrust. They touched down at over 200 kt and 1800 ft/min sink rate. Haynes tried to throttle up at the last minute to attempt some kind of a flare, but one engine responded quicker than the other causing a roll that made the right wing hit the ground first.

@RussellBorogove I checked most of topics similar to this , someone edited the title, and it now looks like a duplicate topic , but the content/question is different.

Gotcha - I probably should have just noted it as related. https://aviation.stackexchange.com/questions/39020/can-pilots-land-an-aircraft-with-only-the-use-of-throttles

In the case of UA232, the horizontal stabilizers had been damaged and there was a continuous tendency to turn right (that's from the report.) According to Wikipedia, fully asymmetric thrust only barely corrected this. That doesn't leave much margin for any other control actions.

Q: So, what is your opinion on landing at Sioux City? A: It SUX.

@RobertColumbia: Well, landing at Rapid City is KRAP.

in the 747 crash in Japan in 1985, the rudder was severed from the fuselage and the pilots managed to keep the plane in the air for about 20 minutes after the failure by differential throttle. However, they could not fully control the plane this way and it eventually flew into a mountain.

Some airliners have in fact landed more or less successfully using only engine power for control. The 2003 DHL attempted shootdown incident is an example.
A major difference between United 232 and Fullerton's landings you cite is that Fullerton was working for NASA testing a system designed specifically for the purpose of assisting pilots in controlling an aircraft with power alone. United 232 had no such system. See https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-041-DFRC.html

Apparently, I missed the point that F-15 had PCA system specifically built for differential thrust assistance. Thanks!


text:
What are the differences between the MiG 31 and MiG 25 (if any)?
What are the differences between the MiG 31 and MiG 25, they look exactly the same, their overall performance the same. Is it the roles they were built for are different?

According to the specs, the answer is: MiG 6

Look the same?? All airliners look the same then! There are more similarities between A320 and B737 than between these MiGs.

The MiG-31 is an all new design with higher strength for low-level flight and new engines. The reason it looks just like the MiG-25 has to do with the structure of the Soviet aviation industry. The basic shape is first defined by the Central Aerodynamic and Hydrodynamic Institute (TsAGI is the abbreviation of its Russian name) and then given to the design bureaus which do the mechanical design. Production is then relegated to dedicated manufacturers which build the designs of different bureaus in parallel.
Both aircraft were designed as interceptors. The main difference is the advanced radar, digital data links and the more powerful engines of the MiG-31 which made a longer fuselage necessary. The MiG-25 radar, a development from the 1960s, could only detect high-flying targets, while the Zaslon radar of the MiG-31 can also detect and track low flying aircraft (look-down/shoot-down capability); a necessity after NATO changed its strategy to nap-of-the-earth flying to avoid detection.
If you need to tell both apart on pictures, look for these features:

While the main landing gear of the MiG-25 has a large, single wheel, the main gear of the MiG-31 uses two smaller wheels in a staggered arrangement.

MiG-31 main landing gear (picture by Burkhard Domke source)

While most MiG-25 were single seaters, the MiG-31 has two occupants, a pilot and a weapon systems officer behind him. Two-seater versions of the MiG-25 can be easily distinguished because the two cockpits are separate units, the front cockpit replacing the radar.

MiG-31 on the ground with canopies open (picture source)

The wing root of the MiG-31 has a small strake added while the wing of the MiG-25 is a pure trapeze with a straight leading edge. The picture below shows the MiG-25 in black lines and the MiG-31 overlaid in red.

Stud points for the amazingly detailed answer

@David: And I thought I left many details out to make it more concise.

I saw a good documentary about Mig-25 and Mig-31 on Youtube not long ago. Worth seeing, it explains a lot of details, decisions and initial problems they had.

Answering it from another point of view,
the MiG-31 had to be the better MiG-25 mixed with the advantages of the Tu-128
As the Successor of the Tu-128 (the Tu-148,T-58M / T-6 and the Yak-33) did not work out, the MiG OKB was the only one left to build a new far range Interceptor
With the possibility of using a new engine, the D30F, bigger ranges, slower landing speeds the E-155M emerged
different materials were used, more titan (8%->16%) and light alloys (11%->33%)


text:
What is this open panel at the rear of this airplane?
I saw this photo at another interesting question:

There's an open square panel. What is it?
P.S. Any tag suggestions are welcome. All I could think of was "tail".
EDIT: are there any other tags for this kind of thing? The APU tag seems to be a crystal ball because I had no idea what it was at the time.

I'm guessing it's APU related.

Next question

It is the Auxiliary Power Unit (APU) inlet door.

Image from Boeing Aero Magazine

Next question: why is does the inlet face upwards, where rain can get in? If it opened downwards, they wouldn't have to put a door on it at all.

@steveverrill I don't think the door is for rain protection but for aerodynamics. Afaik the APU is not used in-flight. So you can cover the inlet with a door because a "hole" in the fuselage would generate drag.

it if were facing down, it would be subject to FOD. it probably has an inertial separator not just for rain, but for debris as well.

oh and here i thought the question was asking about the square open panel below the tail number and door... @DrZ214

@steveverrill Rain isn't usually a problem for jet engines. FOD is, though

@TomMcW Sure I missed the possibility of FOD, but the reason rain isn't usually a problem for jet engines is because they're normally horizontal and have a fairly straight flow path. Undrained water collected in intake of any type of engine while stopped can potentially cause damage on startup, as well as corrosion while shut down. If door was damaged, and there was significant rain while APU was stopped, I'd want to check it before flying on it. It's possible there's a drain line to prevent water collecting in the intake, but I cant see it in the drawing, nor can I see an opening in the photo

@steveverrill Yeah, it's prob not advisable to let water sit in there while it's not running. I'm assuming the door is normally only open when the apu is in use. So preventing rain ingress may be one reason the door is there. The diagram does show a drain for the exhaust, though. I guess because it can't be closed.

@Michael oops, i ddnt even notice that tiny one on the underside. I thought the one with the blue stripe was the only open panel in the photo.


text:
Why don't large commercial airplanes have electric motors in the wheels?
The cost of jet fuel during taxiing can be a pain. Concorde in particular had very large fuel expenditure for taxiing.
So why not put electric motors in at least 2 wheels to drive the plane that way? They would not have to be the most powerful motors in the world---only strong enough to get the plane up to a few miles per hour, or normal taxi speed.
EDIT: I don't think this is a duplicate of this other question. If anything, the savings cited in the answer of that question seems to imply that my question, asking why it isn't implemented, is actually a pretty good question.

Well, you might as well guess where the electricity to run those motors would come from; sooner or later, the jet engines themselves.

@SMSvonderTann Yes but unless I'm totally mixed up, power generation from jet engines is much more efficient than small (taxiing) amounts of thrust from jet engines.

How is this question a duplicate? The question of What are the savings of...? is very different than the question of "Why isn't that technology used?

related, perhaps duplicate: Does it make sense towing airplanes to the head of airstrip by external means?

To me this is not a duplicate: the other asks if it would be convinient, this asks why currently it is not the case.

In fact, this is currently on test.
This test is conducted by Airbus, Safran and Honeywell for the Airbus 320 familly on this aircraft.

An engine is installed on the wheels of the main landing gear

As you might know it take long time and lot of money to certified a system in aeronautics, this is why it's not in use yet.
I other hand, you need to run engine in idle for about 5 minutes in order to warm up the engine and stabilise systems (hydraulics, gyroscopes, etc)
You can find more here : http://www.greentaxiing.com/
Edit 1 : edit to add @Ben elements

This doesn't answer the question, "Why...". Has the technology been unavailable? Has the electric power source been weak? Have the existing design concepts been developed only so recently that they are not yet available?

@JonathanWalters "As you might know it take long time to certified a system in aeronautics, it's this is not in use yet.". You can understand "use" by available.

That doesn't look like an electric motor to me. Is that...an internal combustion engine?

@DrZ214 I assure you this is a electrical engine :D

Terminology in English is combustion --> engine (usually), electric --> motor (always.) Apart from that, a good answer.

As Kromen points out, such a system is in development. There are just two main impediments:
1) The not-insignificant costs of design, certification, installation and operation.
2) Jet engines can't just be turned on as the aircraft lines up on the runway. The startup sequence itself can take a few minutes, and then they need to be running at close to idle for up to about 5 minutes to allow all of the aircraft systems (hydraulics, gyroscopes, etc) to stabilise.
These aren't insurmountable obstacles, and the system should have great benefits at busy airports with long taxi times. But this helps explain why it hasn't exactly been a top priority over the years.

Probably increasing emissions / environmental controls have increased the focus here, beyond simple commercial fuel cost considerations.


text:
How are aircraft protected from lightning strikes by conductive skin?
I've read this question and this one, but they don't really answer my question.
How or why are aircraft protected (from lightning) by a conducting skin, such as aluminum? Conductors allow current to flow through you! Wouldn't it be better to have an insulating shell?
I realize its not possible to have an ideal bubble completely protecting you, because the engines need to breathe air. Presumably these metal engines would then take the brunt of the lightning strike.
So let me try an example with a glider. Let's say we have a glider completely surrounded by an insulating skin. Just for the sake of ideal example, let's say this skin is the best material insulator known: diamond. (Okay, it's not solid diamond. It's just a diamond coating. Yes, they can build that via chemical vapour deposition. I know it's not economical, it's just for the sake of an ideal example.)
What would happen if this craft gets struck by lightning? Please don't say "it explodes" without some kind of citation or explanation or I will be suspicious of hollywood falsehood.

I'm voting to close this question as off-topic because it is a question for physics.se (Faraday's cage)

@Federico When you think about it, questions about lift, drag, and engine efficiency can also be asked on physics.SE. They are permissible here because they relate to aviation. I hope we can agree that lightning also relates to aviation.

Conductors allow current to flow through you! this is where your question falls down.  This is an incorrect assertion.

The question is based on a wrong understanding of electrostatics which states a metallic cabin protects the passengers from field (hence current) exactly like a lightning conductor protects a building. Actually today's issue in aircraft design is to recreate this protection where the cabin is not metallic (aluminum replaced by composites). Convincing demonstration on Youtube. Theory of equipotential closed surface.

I don't agree with the down votes. This is a valid question. It just happens that the OP's understanding about its underlying physics is very wrong.

@Simon It would be good if you could elaborate. There are conductors and insulators. One allows current to flow, one doesn't (at least not easily). If you're talking about something like skin effect and want to debate the meaning of the word "through", maybe we could have a go at English.SE.

@DrZ214, English.SE would be useless for this. The problem with "through" is that it depends on where the conductor is. If the conductor is around you, then the current will predominantly flow through the conductor and therefore around you, not through you.

The best insulator (vacuum) is not a perfect insulator. All materials have a dielectric strength, that is a capacity to resist voltages before they loose their insulating properties. Diamond will resist up to 2,000 MV/m. If the layer of diamond is 1 mm thick, it will resist up to 2 MV only, and then it will conduct the electrons. But more critical is that while it insulates, it still allows electric and magnetic fields to exist inside the insulated volume.

@mins Interesting, but you mention a vacuum and then say "all materials have...". Vacuum is not a material. I searched and found (https://en.wikipedia.org/wiki/Dielectric_strength) the Schwinger limit which suggests the dielectric strength of a vacuum is 1 billion MV/m, so I see what you're saying. Interestingly, though, not even this is enough to protect against a positive lightning strike (much rarer than negative lightning, which is weaker), which can go over a billion volts. So even if we could build a protective vacuum shell 1 m thick, it wouldn't be enough!

@TomMcW thank you for creating the lightning tag. I was surprised to not find it when I first posted this. I have a feeling it will come in handy again soon.

(Vacuum is not a material, but I was short of characters) Good additional findings. So actually the best solution (and only one, due to fields... think about EMI weapons...) is to use a very good conductor which can deal with the energy. The idea is to have all points of the protective surface at the same potential (it's not possible, but we can come close). If the shell is a sphere the protection is perfect at the center.

Regarding @Simon comment, you can see being in contact with a conductor is not the problem: Maintenance engineer is filmed crawling along high voltage line


text:
In helicopters, why not have electric motors controlling blade pitch?
From my related question comes this idea of electrically controlled blade pitch in helicopters.
Control linkages in helicopter rotors seem to be pretty complex. This surely incurs a lot of friction, especially if you realize that blades have to "flap" back and forth as they rotate around (in order to compensate for retreating blade stall and/or dissymmetry of lift during forward flight). So the swashplate and linkages must surely undergo a lot of friction.

So why not replace all this with electric motors that control blade pitch? They would be small, inside the rod connecting the blade to the hub. No need for any pitch control to be mechanically connected to any other blade(s), so no friction. A computer would control what the pitch should be given the blade's position during its rotation.
This does not mean the main rotor has to be electrically driven. The turboshaft engines can drive the main rotors mechanically as normal. But there would be an electric generator for the blade pitch motors. Note: I'm pretty sure there's already an electric generator on these engines as the computers and radars and stuff have to get their electric power from somewhere.

What problem are you trying to solve?

Note that your premise "surely incurs a lot of friction" is wrong. This is just a 'rotational' variety on a camshaft you can find in any car; it is in fact an extremely efficient way to prescribe a certain movement. The reason is that there's a microscopic oil film between all components, which reduces the friction to almost nothing. Besides, don't your actuators need bearings too?

@Simon friction and/or wear and tear of the complex hub linkages that control blade pitch. It may not be a major problem, but if it's reduceable then why not? At least, that was the question. "Why not" seems to be answered by now.

@sanchises I take phrases like "reduces friction to almost nothing" with a grain of salt. I'm sure there's lubricant between all moving parts, but unless you have a source saying there is almost no friction when the blades flap up and down during the high RPMs of helicopter flight, I can't believe it. And of course my actuators need bearing. My idea would have one moving part per blade, plus bearings, as opposed to I can't even count the moving parts per traditional blade, not the least of which are the swashplate and control rods.

I have absolutely no idea how much energy is lost due to friction in these parts, but I am equally absolutely convinced it's a rounding error when factored into the energy lost due to drag in the system and friction in the engine and gearboxes.

@Simon I wouldn't be so sure of that either without a source. Friction/resistance at one end can be felt at the other end of the engine, since they're all moving each other. It's hard to separate friction here from friction there when resistance at one end requires the whole engine to push each gear harder  (so each gear gets more friction too) just to overcome the resistance at the end. Again, the blades have to flap 2x per rotation, and the rotors have fairly high RPMs. Doing all that with a swashplate "bumping" control rods up and down seems rather friction-intense to me.

@DrZ214 You would then also think that piston engines are awfully inefficient since they must be bumping up and down. And, for that matter, that trains must come to a grinding halt when going through a curve. The simple fact is that changing the direction of something is not really a problem - whether it's a 10-tonne train going through a curve or a rotor blade flapping up and down. If you don't believe a mechanical engineering masters student, I would advise asking on Mechanical Engineering SE why camshafts are not as bad as you think they are.

Just want to point out that most wind turbines operate this way - electric motors at the root of each blade provide pitch.  Although capable of independent blade control, they generally pitch all blades together collectively, and even then these motors are a significant maintenance issue.

"...significant maintenance issue."  Without any real background on the details this was the immediate thing that popped into my head as soon as I read the title question.  That coupled with safety/reliability.

How would you communicate with (and power) these motors?
The main rotor is spinning constantly - Wires won't work, they would wrap around the shaft and be shredded. A slip ring and brushes (as used in some electically-actuated propellers) would work, but would also wear away quickly and require frequent maintenance as losing control of a helicopter's main rotor blade pitch is a much more serious situation than losing control of a fixed-wing aircraft's propeller pitch (I believe this captures the consequences pretty well).
Because of the rotor speed balance is critical, so any motors, brushes, etc. would need to be balanced around the rotor hub (either by duplicating the equipment, which also provides redundancy, or by adding dummy weight) - get it wrong and the rotor starts vibrating and may come apart.
The motor would also have to be constantly moving: The swashplate adjusts blade pitch through the full 360 degrees of rotation, smoothly changing the pitch of each rotor blade as they rotate. Duplicating this would require the motor(s) to make constant adjustments as the rotor turns, moving and reversing very rapidly). The level of precision required and the forces involved would likely require high-torque stepper motors and a computerized control system of some kind would be needed to drive them and make the necessary blade pitch adjustments at "rotor speed".

So far the motorized solution has added at least one motor, a slip ring & brush system to communicate with it, and a fly-by-wire computer to read the flight control positions and appropriately adjust the blade pitch through 360 degrees of rotation (at whatever speed the rotor is operating).
That is already a lot of complexity and a substantially increased chance of failure versus the (relatively) simple mechanical solution of a swash plate, and I'm not even going out of my way to think of failure modes (actual engineers designing these things are far more paranoid, and could probably imagine all sorts of failure scenarios which eventually result in a helicopter plunging to the ground).

I would rather have a mechanical link, designed, tested and proven over millions of flight hours, for one thing to push another thing, than a nest of cables, computers and motors. +1

In addition to the above mentioned problems, the effect of having to move constantly back and forth at high speed every rotation of the rotor would mean that the complex and more expensive motor would wear out just as fast if not faster than the less expensive mechanical parts. Reversing direction is particularly tough on electric motors because the coil that is active has to remain powered for a longer time creating extra heat on the coil and the associated brush. And the motors would have to reverse themselves twice for every rotation of the motor.

Not sure where the first video "captures the consequences pretty well" was supposed to point... it seems to be a science fiction show not involving a(n) helicopter.

@Michael Listen to the dialog. ("Oh god, oh god, we're all going to die.")

How would you communicate with (and power) these motors? That's a great point I never thought of. And hey don't bring a great show like Firefly into this :-)

Because it would be too complicated (and failure prone) compared to the present system and would offer no great advantages.
First, for all the complexity in the helicopter upper controls, the principle is pretty simple- Align the rotor plane with the (rotating) swash plate, and tilt (or rise) it according to requirements.

Source: helistart.com
This system is used in almost all helicopters, and have operated for millions of flight hours under a variety of conditions and has proven itself over a wide range of helicopter weights.
In order to replace it, the electric motor system should have the following characteristics.

The electric motor, if used should be highly robust, with extremely low failure rate as it (failure of any one) would jeopardize flight safety. Also, it should be able to deliver significant changes in torque in a rapid manner.
The power supply to the motor would be critical and the only thing I could think of is the slip-ring system. This would require frequent inspection as power supply (and signal transmission) is absolutely critical for operation. The power supply required would make the electrical system of the helicopter heavier and more complicated (due to redundancy).
New control algorithms and a flight computer (a fly-by-wire system) has to be developed for this system as it is completely incompatible with the present ones and there is no way to directly transmit the pilot control inputs to the rotor blades as it is done at present. I'm not sure if anyone is going to develop a complicated system (it has to be operational at every point of the rotor rotation as pitch is varying constantly) to replace a system that has been operating well.
The components should be balanced (i.e. their weights should be balanced) across all the bales as it would lead to vibrations otherwise.
The rotor would have to be hinged at some point anyway. Then the question becomes how to transmit the rotary motion from the hub side to the blade side. This can be done either by

Pitch link, which is practically the same as a mechanical linkage, or
Torque transmission through a rotating shaft.

In either case, the system should be able to flex both in up-down direction (due to blade flapping) or in forward-aft direction(due to blade lead-lag movement).
One instance where electric motors are actually used for pitch control is in active vibration control, were individual rotor blades are controlled using piezoelectric actuators for vibration control.
The rotor pitch control you are describing would require control forces which are orders of magnitude above that of Individual Blade Control system used and would require a completely new system. Even in this case (where power requirements are modest), University of Southampton notes,

the dependency of active control on external energy supply can limit its practical applications, particularly in hostile environments, where energy is scarce or unreliable, or where it is impractical to route a power supply.

So, using of electric motors would actually have the effect of increasing cost, weight and complexity of an already working system which is not a good idea in an (critical) aircraft system.

While your outline is educational, the statement that new pitch control system would require control forces "orders of magnitude" above the present system...just seems wrong. Whatever huge control forces resist flapping the blades are already overcome by the swashplate and linkages we have today. Electric motors would have to overcome the same resistance, and maybe even a little less if friction is reduced. So unless there's some sort of huge lever arm hidden in the control rods, flapping the blades 2x per rotation requires the same (huge) force whether it's by mechanical or by electrical.

@DrZ214 I think he meant the forces are orders of magnitude above those of the vibration control system he mentioned, not of the current blade pitch control systems.

@DrZ214 reirab is correct. I was comparing the required control forces for total control of the h/c with those required in active vibration control

@aeroalias okay, i'll leave these comments here in case anyone else had the same thoughts.

I went on a little search on my university library database, and found a review paper. I'm not sure if you can access it without paying.
Active rotor control for helicopters: individual blade control and swashplateless rotor designs by Ch. Kessler. Link: http://dx.doi.org/10.1007/s13272-011-0001-0
There, I extracted three sources relevant to your question:

Kretz, M.: Research in multicyclic and active control of rotary
wings. Vertica 1(2), 95–105 (1976)
Guinn, K.F.: Individual blade control independent of a swashplate.
J. AHS 27(3), 25–31 (1982)
Arnold, U.T.P., Fuerst, D., Neuheuser, T., Bartels, R.: Development
of an integrated electrical swashplateless primary and
individual blade control system. In: 32nd ERF, Maastricht, The
Netherlands, September 12–14, 2006

If you're lucky, you can find a way to access these papers - however, my university didn't seem to have subscriptions to the relevant journals (either way, they weren't in the database).
In all these papers, the main motivation was to reduce vibrations caused by aeroelastic effects. This means that the interaction between blade elasticity and airflow causes unwanted vibrations which cannot be solved by a swashplate, since a swashplate can only actuate frequencies at the number of blades times the RPM. Friction from the swashplate configuration is of minor importance. A swashplate is generally just a set of ball bearings, which have the nice property that the forces on them are always at a right angle, i.e. a centripetal force which does not cause energy losses. The only energy loss is due to rolling friction, which is extremely small (I found friction coefficients of 0.005 in a paper on lubrications) for properly designed bearings. All in all, very minor compared to the massive power needed to lift a helicopter up.
Note that electronic actuators are not particularly efficient in all situations. (following part revised to clear up some confusion:) Imagine lifting a heavy box off a high shelf. Even though strictly speaking, you're doing negative work on the box, you still feel tired afterwards because for human muscles and (simple) electric actuators alike, it costs energy to apply a force. In other words, an electric motor also has to provide the negative work on a system, unless there are energy recovery systems integrated. This was actually proposed in one paper to overcome overheating issues. Furthermore, for a constant force (no work), a constant current flow is still needed in an electronic actuator.
Perhaps I best quote Kessler in his conclusion (shortened):

Individual blade control can alleviate a lot of typical
helicopter problems:
• reduce the cabin vibration by 80% or even more,
• reduce component loads and power required, [...]
That is the good news. And now the bad:
About 58 years of research and development on HHC and
IBC have passed by. And no helicopter is equipped with
such a system. [...] But even for customers it might be difficult to see an advantage of IBC and a payback. [...] An IBC system would surely
raise the purchase price.[...] On the other side,
designs get more and more complex, the swashplateless
concepts are the far end of this complexity. It should be
questioned if this is still reasonable. The advice would be,
‘‘make one step after the other; do not try to do two at the
same time.’’

I upvoted as soon as I saw all those references, even though I could not access them, because you're the first to cite anything on this thread. Also, you explained the swashplate and it's rolling friction to me, but now I would like to know more about where those aeroelastic vibrations come from. Nevertheless, your analogy about 2 ways to brake a car is wrong. A 1,000 kg car moving at 30 m/s (67 mph) has a kinetic energy of 450 kJ. It will require 450 kJ of energy to stop it. Doesn't matter if it's from a regular car brake turning kinetic energy into vast heat onto the brake pads...

...or a regenerative system "absorbing" kinetic energy into an electric generator and into batteries. Both ways need 450 kJ output. One way may be easier and more fail safe and might even have less startup energy, if we can use that term, but in terms of energy, neither one has "energy requirements: almost nothing". Both of them have to do the same output of negative work to stop the car.

@DrZ214 in a braking car, the majority of its kinetic energy goes into waste heat during tire friction against the road, the brake pads do very limited work in the physical meaning of the word.

@Peteris That's the first I heard of that. Do you have a source or further reading link? I'm having a hard time seeing how the brake pads can overheat while the rubber wheels don't seem to wear down all that much. I could be wrong but if what you said is true, it would seem that all the rubber would vaporize before the brake pads start suffering.

@DrZ214 in conventional (non-ABS) hard braking, the brake pads will fix the wheel so it isn't rotating, and you'd see skid marks on the road with the removed rubber. In hard braking with ABS, there would be many separate intervals of hard braking with skid marks interleaved with releasing brakes so the wheel sticks to asphalt once more, increasing friction. During those times of hard braking, the brake pads 'do no work' and receive no heat any more than the wheel rims or car axle does.  Of course, during prolonged slow braking (i.e. cruising downhill) the brake pads do work and will overheat.

@Peteris Two things: your comment is severely off-topic, and except for the case of a complete lock-up of the wheels, completely wrong. I'll make a slight edit to make a more clear point.

I appreciate the effort but I'm still not connecting with your analogy. Of course you still feel tired, and of course it costs energy to apply a force. I know electric motors have to work really hard to flap each blade 2x per rotation, but by the same token, the swashplate has to do the same work too. Whether it's mechanical or electric, the same work of flapping the blades has to be done. So to me it seems like energy cost is not the issue, as both systems have to flap the blades. However, I do understand that my idea would be active control, or active safety, as opposed to passively safe...

...plus I have just realized that during auto-rotation, blade flapping is still going on and the hub does not seize up from that---so maybe friction from the swashplate and related linkages is not as bad as it would appear.

@DrZ214 - When you say blade flapping is still going on, do you mean that pitching is still going on. Blade flapping is the up and down movement of the blade due to aerodynamic forces, inertia, and gyroscopic precession. In an articulating blade hub, this movement is realized at the coning hinge as in the picture in your question. Even in the case of electrical pitch control, flapping, teetering, lead and lag would have to be accounted for. However, the pitching control would have to operate at over 2000 cycles per minute against the rotational inertia of the blades.

A great source for reference material is https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/media/helicopter_flying_handbook.pdf

Development is in progress, just a matter of time:

Source: Helicopters are quieter (translation by Google)

Hi Steffen, welcome to Aviation SE! Your answer is an interesting contribution for everyone following the link, but runs the risk of being removed due to our preference for answers which contain more than only links. Please consider to write the gist of the linked page into the answer (you may leave the link) so that the answer will be of worth even when the linked page is taken offline.

This is a really great find, please do not remove it!

Okay, sory for the short response. So actually ZF Luftfahrttechnik GmbH from Germany (some of the above cited publications came from ZF, e.g. Kessler and Arnold) is working on the development of swashplateless electrical individual blade control for several years. As far asI know they were the first company working on such actuators. Nevertheless there is similar research going on in USA and China.

Biggest simplification and weight saving would be to totally eliminate the whole mechanical collective & pitch mechanisms and use electrically activated controls to move self energising control flaps on the trailing edge of the blades to drive the required blade pitch alterations in the manner of the Kaman K-Max intermesher - a very successful helio with many years of proven service.

Hi John, welcome to Aviation.SE. Unfortunately your answer does not seem to directly address the question, but rather it seem to promote discussion. This is not considered well here, as this is not a forum, but a Q&A site. You're welcome to stick around, though, and as soon you will have a little more experience of how things work here (and "reputation") you will be able to join us in chat, where discussion such as this are more than welcome.

This answer could be improved by explaining the intermesher design in more detail. As it stands, it only adds a term to the discussion without explaining it. As such, it will risk to be removed.

You may add references for people wanting further readings. It helps increasing the quality of each post on this webwite.

Although I agree with others that the quality of this post needs improvement, I voted not to delete this one as I think there is some value in this answer.

@PeterKämpf I noticed 2 terms without explaining: "Kaman K-Max intermesher" and "self energising control flaps on the trailing edge of the blades to drive the required blade pitch". That last one sounds dubious to me. Sounds like a control surface that changes pitch to change the pitch of the blade itself. To me that sounds either impossible or physically very very inefficient. If you already have an electric servo to change pitch of a flap, why not just change the whole blade pitch that way instead of a flap on the blade.

@DrZ214: The self-energizing part sounds a little dubious, but the rest is standard. By deflecting the control tab the blade is torqued into the right angle of attack. Helicopter blades are surprisingly floppy. But in one we all agree: The answer needs more meat.

Helicopters certified for IFR must meet the requirements of 14 CFR Part 27 Appendix B, which specifies certain static and dynamic stability that can only be achieved through the use of electrical systems to control the rotor system.
There are a number of different kinds of systems which are used to achieve this certification, and all of them use either electric or electro-hydraulic actuators to achieve stability.

I flew an aircraft which had an electric pitch change without rubbing parts, i.e. it changes by electrical induction. Far too slow, and too complex.  Nowhere near fast enough for use in a helicopter.
Sometimes there is a special art and beauty of simple direct or hydraulically boosted linkages.  Especially when it all had to be sent via a rotary coupling.


text:
What are the advantages of dual counter-rotating rotors vs coaxial rotors?
It just seems to me, as though, dual counter-rotating rotors are a much better solution (Chinook) than coaxial and that the center of gravity is offset to allow useful loads to be spread out. Even though that the airframe needs to be longer, does this give more stability on the whole airframe and if so, would engine failure allow for proper auto rotation? I am thinking of small two-four person model for this question.

As if one rotor wasn't difficult enough, you're proposing to incorporate all the extra weight and complexity of a second rotor just to lift two people off the ground. This isn't a practical idea.

@ CatchAsCatchCan you are right if conventional power is used, I was pondering electric as that has much more weight involved and so I thought this may solve that issue.

If your problemmis to lift a big payload then a second rotor might be a solution. The Chinook has been doing that for decades. If the problem is that your power source is too heavy, then a second rotor doesn't solve the problem, it just adds yet more weight. If you're thinking about the various air taxi projects that have six, eight, or more rotors, then they benefit from a mechanically simpler control system, and from some resilience in the event of a rotor failure. They don't really solve the problem of a heavy power source.

Counter-rotate Picture above from this answer, which compares the Chinook with the V-22 Osprey, another counter rotating twin rotor.
For a given weight, the larger the rotor the less power is required for generating the necessary thrust. And here is where a single rotors' advantage is, one single rotor requires less power than two rotors with half size each. In the hover, the single rotor throws away about 10-20% of the engine power to drive the tail rotor, but in cruise flight much of that torque compensation is generated by the vertical tail.
Yes the payload location range of the Chinook config is without equal. In case of one engine failure, the remaining engine can drive both rotors since they are coupled by a shaft. Autorotation is not an issue either - from this thread:

Chinook is extremely docile in handling, yet extremely maneuverable when light. Autorotation is of the thistledown type, rotor inertia is massive and the beggar wont come down fast even if you want it too. Engine off landing is merely a continuous flare to a running landing on the rear wheels which requires quite a lot of runway. I dont know if the military use other techniques.

So in short, the Chinook config has pros and cons. The two rotors' wakes intermingle with a reduced power efficiency in forward flight. From same thread as above:

Due to the dynamics the Chinook develops maximum translational lift in sideways flight to the left, hence the antics of the logging machines plugung sideways on the end of theit long cables - gives them greatly increased lift capacity.

So yes the twin counter rotating rotor does not spill tail rotor power during the hover and has a large payload range. It has a longer but narrower footprint than a similar MTOW single rotor. But it is not universally more power frugal than the single rotor config.

Co-axial. Picture above from this question.
The co-axial setup main drawback is its complexity. Counter rotating shafts, one in the other. One rotor quite high over the other one to allow relative flapping. Super complicated control actuation.
Power requirements: the coaxial configuration has power requirements according to this answer.

All in all, the counter rotating setup is simpler than the coaxial setup, which does have the advantage of a very small footprint. But the single rotor set-up has proven to be the configuration with the best design balance.

The main advantage of the co-axial is speed.  Its more stable a higher speeds as the drag is evenly distributed to both sides.  At cruising speed a co-axial setup can roll, pitch and yaw in both directions easier than a traditional tail rotor design. Its believed to be the main reason why the Russians chose the more complicated setup for the Ka-50/52 so that it could better dodge MANPADs. It comes at the cost of higher maintenance and reduced lower speed maneuvering capability.  At lower speeds the traditional anti-torque design provides better control.

Counter-rotating rotors are safer than coaxial, there is no risk of blade collision during vigorous maneuvers.
Counter-rotating double rotors may have a much simpler head design than coaxial.
There are two types of counter-rotating double rotors.
The first is the tandem rotor used on the CH-47 Chinook. It has a larger disc area compared to a coaxial one and can give a higher lifting capacity, especially when blade span is a limiting factor.
The second is the intermeshing rotors used in Kaman machines. It also has a larger disc area (although smaller than that of a tandem rotor), but helicopter with intermeshing rotors may also be lower.
For a small helicopter, the tail rotor is the optimal choice due to its simplicity and low cost. When safety considerations are the dominant factor, intermeshing rotors are the best choice.


text:
How can I calculate the maximum range of an aircraft descending with power (not gliding)?
Let's assume I have an aircraft, for which the thrust is not enough to keep the altitude. So over time I will lose some altitude. But it will still go further then it would without having an engine (gliding).
How can I calculate the maximum possible range for this case?
I know the Breguet equation, but I do not think this helps me in this case?
Some formulas would be great.

I think you may find interesting elements on the section about power curve of the resource "how it flies?"

You can use the lift to drag ratio (L/D) to calculate for just about any stage of flight if you compensate it properly. Assuming your descent is steady-state, lift is equal to weight, using the L/D you can then determine drag. Next take drag and subtract the thrust produced by the engine to get the amount of excess drag need to be covered by gravity. You glide ratio will be lift divided by excess drag. This makes for a simple calculation of your variables remain constant, however you will need to use an integral if you want to compensate for changes such as differences in engine power at different altitudes, and reduction in weight as fuel is burned.

You ultimately want the glide angle, so we can just look at the equilibrium equations for the glider as a starting point. I will assume a quasi-stationary, wings-level.
$$
L=W\cdot \sin{\gamma}
$$
$$
D=W\cdot \cos{\gamma}
$$
where $\gamma$ is the glide angle, positive downwards. This leads to the self-evident:
$$
\tan{\gamma}=\frac{1}{E}
$$
Which just says that the glide angle becomes shallower with increasing aerodynamic efficiency.
If we add in a thrust component to our glider, we can redo the above for a powered glide:
$$
L=W\cdot \sin{\gamma_p}
$$
$$
D=W\cdot \cos{\gamma_p}+T
$$
which gives:
$$
\tan{\gamma_p}=\frac{D-T}{L}= \frac{1}{E} - \frac{T}{L}
$$
This is dimensionally sound and, more importantly, converges to both the original glide angle equation for $T=0$ and to $\gamma=0$ (horizontal flight) for $T=D$.
For either angle, knowing your starting altitude, you can obtain the glide range as:
$$
x_{glide}=\frac{h}{\tan{\gamma}} \left( \approx \frac{h}{\gamma} \space \text{for small angles} \right)
$$

Well, sir, at steady state, (no acceleration, forces balanced), (using the Lift equation), does $Lift = Weight$ at a given airspeed and trim regardless of orientation.

Lift does not equal weight in a glider, you got a number of decent answers on that front here, maybe you should review them?

well, as we advance our state of the art, we come to realize Lift has NO relationship to climbing, descending, powered or gliding. It is based on coefficient of lift (airfoil type and AOA), airspeed, and wing area.  So, former answers go by the wayside, or are improved.  Continue to learn so much here. I will review your equations.

At a given airspeed, your plane (not only the wings, but the entire plane) will have an optimal L/D ratio. That's also the glide ratio. For example, if the best L/D is 10, your airplane, flying in a glide, will move horizontally (at the airspeed for optimal L/D), 10 kilometers for every kilometer of altitude that it loses.

Since engine thrust will improve with increasing density, the effective L/D will also improve as the aircraft descends.

Okay but an aircraft, flying at best L/D will reach a bigger distance with a switched on engine than with a switched off engine.

How do I account for this? And besided: a commerical aircraft, is it always flying with best L/D during horizontal flight?

This answer would be correct for a glide, but power confounds the L/D condition.


text:
What is this type of aircraft?

In this picture, could anyone describe what type of aircraft and which airline it is?

Any type of information on what flight this was? Or source of the picture?

The background is pretty clearly downtown New York; if nothing else, the Empire State building should be a dead giveaway.

That area in the photo is better described as Midtown South.  Downtown is the collection of highrises just below the wing.  -Skip Miller

That's a US Airways Embraer E190
Here is another view of the E190 wing for comparison.

And sadly, CRJ production is winding down toward the end of this year so Embraer pretty much has the market all to itself, perhaps until the Mitsubishi RJ is certified.

@JohnK not so much. The A2xx series from Airbus is what was previously the C-jet series Bombardier designed to replace the CRJ in production.

No the C series is a larger airplane and was not intended as an RJ replacement. It was a bridge between the Regionals and the smaller narrowbodies.  The E jets pretty much have the 70-90 seat market to themselves notwithstanding minor players like Sukhoi.


text:
How can I identify the aircraft’s phase of flight in this picture?
It’s me again, can anyone explain how to know the aircraft’s phase from this picture? Is it cruising or descending if so why its flaps up?

It is much lower than cruise altitude, I would guess roughly 4000-6000 feet.  The flaps are up because it is neither taking off nor landing.  Generally flaps are deployed around 2000 feet or below.  Given the proximity to New York City it is probably flying an arrival or departure procedure.
If you really wanted to dig deeper you could determine relative position and from Manhattan in the background and compare against published procedures into and out of the city's airports.

The airplane's position is over Manhattan, about 50th street heading west.

Less than 10000 feet its speed would be limited.  It may have been light enough to be ok with out flaps.  I would guess departing.

In case anyone's interested, you can come up with a rough estimate of the airplane's height by measuring the distance from the base of the Empire State Building to the horizon, using the Empire State Building itself as a scale. By my estimate, from the base of the building to the horizon is about three and a third Empire State Buildings, and the Empire State Building is about 1,500 feet tall (including the spire), giving us an altitude estimate of about 5,000 feet (which precisely matches what Michael already wrote).

I guessing 3000 ft on an arrival to Newark and is just about to start dumping flap in the next minute or so.


text:
How do I use the takeoff and landing distance charts in the C172 POH?
Can anyone explain how to calculate takeoff and landing distances using the chart for C172s, and please give me an example?

If you have an iPhone or iPad, there is a free App called "C172 Performance". I often use this before I fly a C172.  https://apps.apple.com/ca/app/c172-performance/id741721884

Yes, I can. But, this is definitely something best taught in person, or at least in real time. It is not too complex once you get the hang of it. Do you have a CFI you can ask? Also, to what year and model of C172 are you referring? Some POHs have a textual table to calculate each of those performance figures. Some have a complex looking x/y-axis graph.

You can also find an explanation here https://aviation.stackexchange.com/questions/13129/what-are-the-meanings-of-various-reference-lines-and-sections-in-a-take-off-dist

There are many ways to calculate aircraft performance. Some ways are entirely manual through the use of formulas. Some ways use electronic means like apps and special calculators. Some ways use pre-calculated Tables. Then there are ways that use graphs and charts. Let’s tackle the charts way.

First, remember one thing. These charts are made from data obtained using highly experienced and skilled test pilots using brand new airplanes with ideal performance and under ideal conditions. Since you probably meet none of these parameters (most of us don’t), it is best to add as much as 50% fudge-factor to your results as a safety buffer.
Think of the Takeoff and the Landing Performance Charts as each being a combination of 4 separate charts.

The Pressure Altitude to Density Altitude conversion chart.
The effect of Density Altitude on weight chart.
The effect of wind on distance chart.
The additional distance needed to clear an obstacle chart.

To start your calculations, read any associated text on the chart. It will give you parameters that must be met in order to make the chart as accurate as possible. They may also give you factors to consider and/or adjust in your calculations.
The Pressure Altitude to Density Altitude conversion chart.
Next, find out the Pressure Altitude and Temperature at Field Elevation for your point of departure. You may have to obtain the Pressure Altitude by calculating it using your Field Elevation and Atmospheric Barometric Pressure reading. Another chart may be handy for this.
Start your graph entering at the horizontal Temperature axis at your Field Elevation Temperature. Follow the graph line vertically up to where it intercepts the line representing your Field Elevation Pressure Altitude. Follow the graph line horizontally to the right until it intercepts the Reference Line for the next section of the chart.
The effect of Density Altitude on weight chart.
Enter the next section at the point where your drawn graph line from the previous section intercepts the Reference Line. Draw a line that roughly parallels the diagonal lines immediately above and below your drawn line. Find the point at which your drawn line intercepts the vertical graph line representing the actual total weight of your aircraft at the point the performance data would be used (takeoff weight or landing weight). Draw another line horizontally from the point of interception, to the next Reference Line.
The effect of wind on distance chart
Enter the next section at the point where your drawn graph line from the previous section intercepts the Reference Line. Draw a line that roughly parallels the diagonal lines immediately above and below your drawn line. Find the point at which your drawn line intercepts the vertical graph line representing the actual Wind Component at the point the performance data would be used (takeoff or landing). Draw another line horizontally from the point of interception, to the next Reference Line. If the winds are calm, use the 0 wind graph line that coincides with the Reference Line. Your drawn line would then be an individual horizontal line from the reference line to the next Reference Line.
The additional distance needed to clear an obstacle chart.
Enter the next section at the point where your drawn graph line from the previous section intercepts the Reference Line. Draw a line that roughly parallels the diagonal lines immediately above and below your drawn line. Find the point at which your drawn line intercepts the vertical graph line representing the actual obstacle height AGL you would have to navigate/avoid at the point the performance data would be used (takeoff or landing). Draw another line horizontally from the point of interception, to the vertical axis on the right. If there is not an obstacle, use the 0 height graph line that coincides with the Reference Line. Your drawn line would then be an individual horizontal line from the reference line to the vertical axis.
Results.
The value you read on the y-axis of the chart is the minimum distance you need to accomplish the stated phase of flight under the given conditions. As a reminder, there will be different charts for different phases of flight. A phase of flight may have multiple charts. An example of this is a chart with flaps and a chart without flaps. Make sure you are using the correct charts and conditions for your aircraft and situation.

This comes from the Cessna 172R POH and is typical of takeoff and landing performance calculations for all Cessna 172s.
First off READ ALL OF THE RELEVANT NOTES IN THE PERFORMANCE SECTION of the AFM as they explain this in detail.

But as an example, let’s assume we are departing Gerfield County airport in Rifle, CO (KRIL).

It’s a warm spring day in early June.  The local METAR reads.
KRIL 022006Z AUTO 06308KT P6SM SKC 22/08 A3016 RMK A02.
As loaded, our C-172R airplane weights 2247 lbs at takeoff.
The second step in any kind of preflight work is to GATHER ALL THE RELEVANT DATA.  Here, we’re going to need the chart supplement entry for KRIL as well as the Airplane Flight Manual for the C-172R.

From the sectional and the supplement, we see KRIL has a field elevation of 5537 ft.  The runway is paved and 7000ft in length with a 1.0% grade up heading east. The winds were 063 True at 8 knots (local mag variation is 10° E, so this is 053 @ 8 kts).  Using a E6B gives us a takeoff headwind of 7 kts).  Local temperature was 22°C.
Let’s follow POH recommended procedure here and select the next higher value listed in the takeoff performance charts.  The field elevation was 5537ft, so we’ll select 6000ft.  Local surface temperature was 22°C, so we’ll use 30°C.  Using an E6B, we can determine with a field altimeter setting of 3016, the pressure altitude will be 5297 ft.
ALSO NOT WELL ANY ADDITIONAL NOTES AND ANNOTATIONS ON THE TAKEOFF DISTANCE CHART.  Specifically, for these calculations to work for you, you must have a paved, level runway, have the mixture leaned to maximum RPM, and use the recommended short field takeoff procedure listed in Section 4 of the POH!
In our case we do have a paved runway, but the winds favor using RWY 8, which has a 1.0% upslope to it.  This will increase our takeoff roll as we are traveling uphill.
From the takeoff distance chart entry for a pressure altitude of 6000ft and 30°C,
Takeoff roll: 1880 ft
Dist. to clear 50ft obstacle: 3590 ft
Note as well that we have a 7kt headwind, which, following the notes, gives us:
Corrected takeoff roll: 1744 ft
Corrected dist. to clear 50ft obstacle: 3330 ft
We also have a 1.0% upslope to contend with and the POH offers no advice on this except the takeoff numbers only apply to flat runways.
My advice here: I always include a 30% Factor of Safety in my calculations as POH numbers were prepared in a new airplane flown by experimental test pilots under ideal conditions.  My airplane’s condition combined with my piloting technique may be deficient compared with ideal standards.
Using this, we find:
Final takeoff roll: 2268 ft
Final dist. to clear 50ft obstacle: 4330 ft.


text:
Does every control surface need to have a counterweight?
Is it not a good idea to balance all control surfaces, no matter what they weigh?
I am building a small plane, with small control surfaces. There are many of the same type of plane flying. Most have no type of counterweight "balance" on the elevator, or rudder. I am told that is because the surfaces are small and light.

Welcome to aviation.SE!

It depends totally on the size and speed of the aircraft what forces it'll encounter in the first place. IMO It's obviously not always a good idea to increase the load on (especially) control surfaces with additional mechanisms. The is the reason why a 747 has split rudders while a 737 doesn't.

Flutter is an energy storage and release phenomenon.  Surface moves, applies a load to the fixed surface it's attached to, fixed surface bends under the load, stores some of the energy like a spring, then releases it in moving back to its original position, and some of this released energy is transferred to the moving surface attached to it, which is also stored and released back into the fixed surface in a way that adds more total energy than the first time, magnifying the original movement, repeat, and away you go.
For the this to happen the moving surface has to be unbalanced with a fair amount of mass away from the hinge line, the fixed surface has to be flexible (spring like), the whole system has to have a natural frequency that is close to the frequency of the natural oscillation frequency of the moving surface, and there has to be enough energy present in the first place to get the whole thing going.
Generally airplanes that go less than say 80-100 mph don't have the energy to induce flutter if there is reasonable stiffness in fixed surface like the horizontal stab.  Light airplanes with fabric covered wire braced tails have stabilizers that are quite stiff due to the wire bracing, and the combination of high natural frequency resulting from the rigid system and the low input energy at the speeds they fly at means they don't really need a balanced surface (look at a Champ's unbalanced elevator; the C of G of the surface is probably at 30% of chord - no big deal because it simply can't excite sympathetic movement in the stabilizer it's attached to at the energy level present at its operating speed range).
If the fixed surface is not so stiff, the moving surface is really heavy, or you want go faster, then you start having to consider mass balancing.  To really know for sure what the threshold is, you'd have to have someone that knows what they are doing do the analysis. But generally low speed light airplanes have the inherent rigidity to be immune from flutter in their speed range without balancing control surfaces.
You still have to confirm it in the real world though.  When you test fly your creation, you do some rudimentary flutter testing by diving to a speed a bit above your Vne (actually creeping up to it in a series of steps), pull up so you are decelerating, and as you pass the speed of your test point you slap the control stick sharply, trying to induce an oscillation.  By doing it while decelerating, the risks of an oscillation starting and building into full fledged flutter are low. But, if you see an oscillation that starts but then goes away, well you've "tickled the tiger's tail" and you'll need to balance the surface or reduce the airplane's speed range.  You're wearing a parachute while doing this of course (or whomever you're able to talk into doing your test flying).

It is better to increase speed in steps, excite the motion and test for the time of the oscillation to die down. Graph that time over speed and you can extrapolate at what speed flutter will occur. Diving to an untested speed for flutter testing is poor advice.

Yes you are right.  I've edited my post thanks Peter.  In any case, I think it's safe to assume someone will research the proper procedure and not proceed based on a posting by an anonymous nobody on the internet ;)

Not necessarily if the aircraft flies slowly so forces stay small. But it is better to have balanced control surfaces.
Now imagine that you fly through a vertical gust and the aircraft pitches up, then down. Since it rotates around its center of gravity, the tail will make the largest excursions from a straight line. Now imagine the elevator has no mass balance. When the aircraft pitches up, the tail goes down and inertia will cause the elevator to lag behind, so you get a trailing-edge up deflection of the elevator. This increases the pitch motion!
On the way back, when the aircraft pitches down, the tail goes up and the same happens in reverse: Now the inertially induced elevator deflection will push the tail further up.
If you now add a mass balance, the elevator stays at a constant deflection angle while the tail bounces up and down, causing smaller excursions and improving pitch damping. This makes for a smoother ride and lower loads.
However, if the aircraft flies slowly and you have some friction in the control linkage, the elevator will move less and stick forces will be low so the pilot can add the remaining force to keep the elevator from moving. Adding a mass balance would still be beneficial, but not crucial.
By using some tricks, you can even balance your elevator without adding extra mass. Given a T-tail and pushrods, give the pushrod going from the base of the vertical up to the elevator just the right gear ratio so its mass will balance that of the elevator. If the elevator itself is stiff enough in torsion, that is already enough for a proper mass balance.
Mass balancing becomes essential when you move up to speeds where flutter becomes likely. Small, slow planes are normally too slow to experience flutter.


text:
Can I transfer TSA approval between flight schools?
I have finally been approved by the TSA for my current school and it has not been one month.
If I decide to change the flight school, can my TSA can be transferred fast without any fee?

Welcome to aviation.SE! If your school is part 61, we already have a question about that.


text:
After passing a checkride, can I get the plastic certificate card by visiting the nearest FSDO?
As you know, it takes more than 30 days for the plastic certificate card to be delivered. I know that right after passing check-ride, the temporary certificate is given but I need a plastic card to convert US pilot license to my country license. My government does not accept the temporary paper certificate. Is there any way to get a plastic certificate card from the nearest FSDO as fast as possible?

No, sorry. They don’t have the device at the FSDO that would produce a plastic card.
If you want to see the page that shows what date they are currently processing for, click here.
Unfortunately it’s typically around 6-8 weeks.

No, FSDO's do not issue the plastic cards. Your only option is to wait.
Processing time takes quite a while. For example, it is November 13 and the FAA is currently processing applications that were submitted on October 3. The process to actually receive your plastic license can take from 30 days (unlikely) to over 3 months. I think on average the time from application to license in your hand is about 60 days.

Hmm.. I’d better check in with them. I got my UAS certificate more than 90 days ago and still haven’t got my plastic card.

@Canuk Look up your info on the airman registry. If your information is there, the application has probably been processed and you should have received the card (within a couple weeks of that status updating). If you haven't, I'd apply for a replacement.

Found out there was another reason.  Just takes a long time to transit information between Oklahoma City and my local FSDO, apparently.


text:
What happens if an aircraft is only stable at higher angles of attack?
Does anybody know what will happen to an aircraft, if it is stable (in longitude) for let's say: -8° > angle of attack > 8° ?
So for angle of attack 4° the aircraft is not stable (centre of pressure is in front of centre of gravity), so the angle of attack will further increase until 8° where it becomes stable (centre of pressure behind centre of gravity).
So except that my aircraft will oscillate a bit, it should always return to a stable position, right?

This question is being discussed on meta: https://aviation.meta.stackexchange.com/q/4193/1467

NB: The question originally included the second part about whether statically unstable aircraft can be flown. I've removed it in an edit to leave only the first, unique part.

I find it hard to come up with an actual example that behaves like postulated. Normally, airplanes are most stable at low angles of attack and lose this stability at higher angles.
But there is indeed one case where angle of attack stabilizes the airplane: A swept flying wing without a vertical tail. Like the Horten designs. Those would enjoy increasing directional stability with increasing angle of attack. Your limits are a bit extreme, but a Horten IV was directionally indifferent at high speed when the typical angle of attack of the root airfoil would be between 2° and 0°. At lower speeds the induced drag would help to pull the airplane out of a sideslip as explained here.
Due to the high inertial moment around the vertical axis this behavior can be controlled by the pilot because sideslip angles will build up slowly. But it is not pleasant since it needs constant control inputs and puts an unnecessary workload on the pilot which might interfere with other tasks like navigation and collision avoidance.
Of course, this example is not quite what you wanted, since a higher sideslip will not stabilize the airplane. Only pulling up will.
If we hypothesize that an airplane behaves as you postulated, it will tend to leave the unstable region, but this might happen both in positive or negative AoA direction. An excursion into negative angles of attack is rather unpleasant (have you ever flown an outside loop?) and will probably make the pilot pull up hard. What happens next? The airplane flies through the unstable AoA region and picks up more pitch speed, only to arrive in the stable region with such a force that it overshoots the AoA limit and either stalls or, given enough flight speed, breaks up.
The Saab JAS-39 Grippen had such an unexpected overshoot at the most unfortunate of times, namely during a flight display on the occasion of the yearly Wattenfestival in Stockholm in 1993.
Any instability in the regular operating region is a bad idea and an invitation for mishaps that could be easily avoided.

If we are going to include directional stability/instability in the answer-- at low angles-of-attack some hang gliders are prone to a dynamic yaw-roll oscillation mode that has a resemblance to Dutch Roll, but may be fundamentally different in some ways, possibly with different driving forces and different relationships between sideslip and yaw rate and bank angle at any given point in the oscillation.  The downforce developed by the wingtips which have significant washout, and the relationship between this downforce and local airspeed which is influenced by yaw rate, may play a key role.

This oscillation is mentioned in at least one book on stability and control but in my opinion is not really correctly described-- hang gliders have both sweep and anhedral, and this dynamic yaw-roll oscillation happens in the part of the flight envelope where the net "effective dihedral" due to the combined effects of sweep and anhedral can be demonstrated to be negative rather than positive-- but better open a chat window to say much more about that--

Would the B-2 also fall into this category of planes in Q? It, of course, has computers stabilizing it's flight and thus does not need pilot focus on maintaining steady flight.

@Jpe61 … and it flies with split ailerons open. This alone gives it sufficient stability. The Hortens also had wing tip spoilers but left them closed until landing.

Answering your second question as originally asked:

Is it possible to fly an aircraft which is not statically stable? I think with a really good control system this should be possible?

The F-16 was designed not only to not be statically stable but to actually have NEGATIVE stability. This means that the aircraft is designed intentionally to move out of its original position (and not return) upon application of some external force, and will continue to move even after that force has been removed. This is a feature of most modern combat aircraft, and it's very possible to fly them, if the aircraft is equipped with a flight computer. Without a computer, it would be very difficult.

Not without a computer.  Downvoted for the implied ease of flying an unstable airplane, and for it being just a partial answer.

@MichealHall partial answers are fine. But with the new edit to the question, his answer is no longer relevant.

@ymb1, I removed the DV for my primary objection, but since it is still a partial answer, and because the question now excludes the quoted portion, I don't think it warrants an upvote...

Notice: The question originally included the second part about whether statically unstable aircraft can be flown. I've edited it to leave only the first, unique part. So no fault on the answerer's part for answering the no-longer-existing part.


text:
Why is the end of the F-35's jet nozzle 'spiky'?
Why is the end of the F-35's jet nozzle 'spiky', is it like that to increase performance or some other factor?

Stealth. The F-35's nozzle is designed in that manner to reduce the IR and radar emissions from the aircraft (sometimes called Low Observable Axisymmetric Nozzle (LOAN)). From the press release which announced the test results:

GE Aircraft Engines' new LO Axi (Low Observable Axisymmetric) Exhaust System was successfully tested recently ... testing being conducted under the Joint Strike Fighter (JSF) Technology Maturation Program ...

According to GE,

... LO Axi Nozzle was installed by the South Dakota Air National Guard in an F-16C and ground-tested to verify installation compatibility with an operational aircraft system. Both infrared (IR) and radio frequency (RF) measurements were made by GE Aircraft Engines (GEAE) with the F110-GE-100 engine operating at power settings ranging from idle to maximum afterburner. The resulting test data verified that the LO Axi Nozzle achieves its installed signature goals during operation.
In addition to geometrical shaping and special materials for signature control, the LO Axi Nozzle also incorporates an ejector that enhances nozzle cooling.

The system was originally tested on a F-16. The following image shows the nozzle while it was under testing

Detailled rear view of a standard P&W F-100-200 still installed in the LOAN aircraft and the LOAN nozzle in the foreground (LMTAS photo); image from f-16.net


text:
How is a "fast jet" classified?
In the book 'Pocket guide to military aircraft', they use the term 'Fast jet' for a certain range of aircraft.
Is 'fast jet' a common and well defined term used within aviation? If so, how is it defined? In order to be classified as a 'fast jet', does an aircraft have to be able to reach a certain flight level, speed or other performance indicators? Does it need a certain engine type? Must it look in a certain way?

Nearly every military plane I know of, I saw them in that guide ( I don't really use my other 5 aircraft books )

@anonymous Can you give and excerpt from the book that uses this term? It would be more helpful in that case.

I have noticed that in British military usage, the term fast jet is common, whereas in American military usage, it is not.  This may be a case of first identifying which class of jargon you are hearing or reading.

Jet planes often have what is called "fast cruise" which seems to be a speed above the optimal cruising speed and near the top of the design specs for speed.

A guess would be "fast jet" indicating a jet that can achieve supersonic flight, ie. most modern fighter jets (F-16, F-15, F/A-18, Su-27, Typhoon, etc). Other jets that cannot reach supersonic, might be called "slow", although most are still fairly fast in their own right (A-10, B-2, B-52, Su-25, etc)

It's a jolly good question. Jet engines are by definition used when the design speed is higher than what is practical for propellers, so every jet is fast. Some are faster than fast, and there are of course the fastest. But Fast Jet sounds like White Snow to me.

There is no accepted technical term called fast jet. However, this seems to be used in media and other uses, especially in the case of British jets. Most of them seem to refer high speed aircraft (BAE hawk, for example). This conference to be held in London, for example repeatedly refers to fast jets:

BAE Systems provides cutting-edge electronic avionics systems .... Its display systems offer fast-jet pilots a real-world view...
AMPA is used extensively across the RAF from fast jets and helicopters ... (A) pilot following the Fast Jet training system will use AMPA at every stage of their training involving Tucano, Hawk T1 and Hawk T2 aircraft before moving on ...

The British seem to use it regularly, for example for the Hawk advanced trainer:

BAE Systems ... said, “... increase the Indian Air Force’s fast jet training capacity and establish a similar fast jet training solution for the Indian Navy. The Hawk AJT fast jet training solution enables an Air Force or Navy...

My guess is that the usage of term is mostly found in UK (the book also appears to be from there). There doesn't seem to be any consistency in usage. While the examples above include the Hawk among others, another media report (UK again) refers to Dassault Rafale as a fast jet:

French Navy Fast Jet Duo set to thrill Air Day Crowds...

To reiterate, I'm not aware of any precise technical term called 'fast jet' and this seems to be (mostly) a British thing.

In UK Air Traffic Control, the term has particular meaning as per CAP 413 (The CAA Radiotelephony Manual):

When receiving an ATS surveillance service, certain ex-military
  aircraft types have been granted a CAA exemption from the Air
  Navigation Order requirement to fly at an IAS less than 250 kt below
  Flight Level
  100. In order to alert the controller to this higher speed profile, pilots of exempted aircraft shall, on initial contact, prefix the
  aircraft callsign with ‘FASTJET’ or ‘FASTPROP’ (depending on
  propulsion type), e.g. “Kennington Radar, FASTJET G-ABCD request
  Deconfliction service”. Use of this prefix shall be confined to
  initial contact with ATC agencies for periods of flight during which
  operations at airspeeds in excess of 250 kt are intended. Once
  acknowledged, it will not normally be necessary for pilots to use the
  prefix in subsequent transmissions until making initial contact with
  other ATSUs.

In my experience, Fast Jet will generally be used to refer to pretty much any jet powered single or dual seat (i.e., non passenger carrying) aircraft


text:
What is this aircraft, when was it produced and used and what was its role?
What aircraft is this, when was it produced, used operationally, and what was its role?

If you just look at the main landing gear arrangement, you may start suspecting it's a Tupolev :)

It is a Tu-128.
In particular it seems to be the "UT" (training) variant:

Image source

Full-scale production of the aircraft began in 1966, with 188 Tu-128s built to 1970, that total apparently including the prototype. Ten "Tu-128UT" trainers were built as well, with a new cockpit for a flight instructor fitted into a swollen nose.

Other info on wikipedia

The Tupolev Tu-28 (NATO reporting name Fiddler) was a long-range interceptor aircraft introduced by the Soviet Union in the 1960s. The official designation was Tu-128, but this designation was less commonly used in the West.

[...]

The Tu-128's only publicly reported combat operation was the destruction of NATO reconnaissance balloons. The aircraft remained in service until 1990.


text:
When there is a holding pattern assigned by a civilian airports ATC, do military aircraft get first priority over landing?
When a military aircraft is landing at a civilian airport, and a holding pattern is in place, do military aircraft get to skip the que, or join in earlier in the holding pattern?

"It depends". Your question is unfortunately too broad to be answered. You should specify what you mean by "military aircraft". Is that simply aircraft owned by the military, or aircraft on an active military mission? If so, which mission? Are they exempted from ATFM? What is the reason for the airborne delays being enforced? And finally, which country or area are you interested in?

@J.Hougaard we already added the caa-uk tag

I can offer this data point. I was an A7E driver for the US Navy and had the chance to do many cross countries. Only a few civilian airfields were ever used on these. There were several reasons for not using civilian fields. One had to do with contract fuel prices, and another with the lack of the starting units our aircraft required. The last reason was there was almost always a military base where we needed one. I landed at 3 civilian airports, one an international airport, and we were handled like any other aircraft. This is just my limited experience though.

@Aaron: OTOH, when we kept the Cherokee at an FBO at RNO, it wasn't uncommon to share the ramp with everything from F-14s to C5-As.

In the absence of any extenuating circumstances (emergency, min fuel, or operational requirements), all aircraft are treated equally and are sorted as per ATC requirements.  If ATC establishes a hold, aircraft will be stacked in (typically) 1,000' increments down to the altitude depicted on the approach plate.  The lowest altitude aircraft is the highest priority, military or civilian.


text:
How can this single-prop drone maintain stable (rotating) attitude and position?
The short BBC news item and video The drone designed to fly on one propeller shows the flight of something that looks like quadcopter missing three of its propellors and motors. It continuously rotates around a vertical axis through its center of mass tilted at perhaps 30 degrees, and the single propellor can provide different lateral thrust in different directions by (I assume) quickly modulating its power throughout the rotation cycle.
This seems to be only a demonstration of an interesting effect at this point in time, but I'd like to understand how it can retain both stable position and attitude with only one degree of freedom (speed). Yes the attitude is rotating, but that motion appears constant.
So far I haven't found anything to read about how this can actually work. In the video there is a suggestion that this has been calculated and equations are briefly flashed on the screen.
The work is done at ETH Zurich and the Flying Machines Arena.
How can this single-prop drone maintain stable (rotating) attitude and position?
I'm also curious if this is a 'new' effect, or is this a version of something that has been previously demonstrated or at least discussed.

above: GIF made from screenshots of BBC video found here.

above: Screenshots of BBC video found here.

You can read all about it in their paper (which actually reads quite nicely)
http://flyingmachinearena.org/wp-content/publications/2016/zhaIEEE16.pdf
First, the parameter space (so, location of propeller, mass, etc) was searched for a relatively stable solution.
Then, stability is achieve through active control, so indeed by varying propeller thrust rapidly. This is done in a few cascaded control loops; so an 'outer loop' that has a position setpoint, which is then translated to a desired attitude. This attitude is then achieved by varying thrust throughout the rotation.

This is exactly what I'm looking for - thank you! "Abstract— This paper presents the 'monospinner': a mechanically simple flying vehicle with only one moving part. The vehicle is shown to be controllable in three translational degrees of freedom and two rotational degrees of freedom." In addition to the control system, I'd like to figure out from a dynamics point of view how it actually controls all of these degrees of freedom.

@uhoh All of that is in the paper. Of course, a background in control engineering is preferred to understand the specifics. In short, they use a linearized system matrix to get a LQR feedback. I could explain everything in this answer, but that would probably come down to copy-pasting their paper which I do not want to do.

Ya I understand your point. I can see that vertical translation comes from average speed, and lateral translation comes from modulation of the speed with period $1\omega$ where $\omega$ is the period of rotation of vehicle around the vertical, so really I'm just wondering if the "control" of the other two rotational DOF claimed are simply passive, gyroscopic stability inherent of a rotating mass, or if there is something active there. In what way is it actually "controllable" in two rotational degrees of freedom. I'll read the paper and if I can't figure it out I'll ask separately. Thanks!!

I think the spinner is stabilized mostly due to the drag of the trailing 'branch' of the Y shape, which prevents the vehicle from 'flipping' along the axis that is attached to the propeller (say, the bottom of the Y-shape)